Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Effects of the Neuropeptides Pituitary Adenylate Cyclase Activating Polypeptide and Vasoactive Intestinal Peptide in Male Fertility

Background and Objectives: The neuroendocrine system plays a crucial role in regulating various bodily functions, including reproduction, with evidence suggesting its significant involvement in male fertility and sperm development. Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) are expressed in both male and female reproductive tissues, influencing penile erection and regulating steroidogenesis in males. Therefore, our study aimed to compare the protein levels of VIP and PACAP in seminal plasma between healthy controls and sub-fertile patients. Additionally, we sought to correlate the levels of these biomarkers with clinical, functional, and laboratory findings in the participants. Materials and Methods: The study included a total of 163 male participants for analysis. The participants were further stratified into subgroups of fertile and sub-fertile men of four subgroups according to the 2021 WHO guidelines. Seminal plasma concentrations of the neuropeptides VIP and PACAP were measured using human enzyme-linked immunosorbent assay technique. Results: The findings showed statistically significant differences in total sperm count, sperm concentration, total motility, and vitality (p < 0.001) between the fertile group and the sub-fertile group. Specifically, significant differences found between healthy males and oligoasthenospermic patients (p = 0.002), and between asthenospermic and oligoasthenospermic patients (p = 0.039). An ROC analysis showed associated sensitivity and specificity values of 62.2% and 55.6%, respectively, to PACAP seminal levels differentiated between sub-fertile patients from fertile males (p = 0.028). No significant difference in seminal levels of VIP was found between the sub-fertile and fertile groups. Conclusions: Previous research leads to the point of PACAP active involvement in spermatogenesis. In accordance to our study, in human semen samples, we have seen a significance change in PACAP levels amongst patients with low sperm count or with both low sperm count and low motility, hinting at its contribution and acting as a possible factor in this complex process. Thus, alterations in the levels or actions of these neuropeptides have been associated with certain reproductive disorders in males.

The transcription factor VAX1 in VIP neurons of the suprachiasmatic nucleus impacts circadian rhythm generation, depressive-like behavior, and the reproductive axis in a sex-specific manner in mice

Background

The suprachiasmatic nucleus (SCN) within the hypothalamus is a key brain structure required to relay light information to the body and synchronize cell and tissue level rhythms and hormone release. Specific subpopulations of SCN neurons, defined by their peptide expression, regulate defined SCN output. Here we focus on the vasoactive intestinal peptide (VIP) expressing neurons of the SCN. SCN VIP neurons are known to regulate circadian rhythms and reproductive function.

Methods

To specifically study SCN VIP neurons, we generated a novel knock out mouse line by conditionally deleting the SCN enriched transcription factor, Ventral Anterior Homeobox 1 (Vax1), in VIP neurons (Vax1Vip; Vax1fl/fl:VipCre).

Results

We found that Vax1Vip females presented with lengthened estrous cycles, reduced circulating estrogen, and increased depressive-like behavior. Further, Vax1Vip males and females presented with a shortened circadian period in locomotor activity and ex vivo SCN circadian period. On a molecular level, the shortening of the SCN period was driven, at least partially, by a direct regulatory role of VAX1 on the circadian clock genes Bmal1 and Per2. Interestingly, Vax1Vip females presented with increased expression of arginine vasopressin (Avp) in the paraventricular nucleus, which resulted in increased circulating corticosterone. SCN VIP and AVP neurons regulate the reproductive gonadotropin-releasing hormone (GnRH) and kisspeptin neurons. To determine how the reproductive neuroendocrine network was impacted in Vax1Vip mice, we assessed GnRH sensitivity to a kisspeptin challenge in vivo. We found that GnRH neurons in Vax1Vip females, but not males, had an increased sensitivity to kisspeptin, leading to increased luteinizing hormone release. Interestingly, Vax1Vip males showed a small, but significant increase in total sperm and a modest delay in pubertal onset. Both male and female Vax1Vip mice were fertile and generated litters comparable in size and frequency to controls.

Conclusion

Together, these data identify VAX1 in SCN VIP neurons as a neurological overlap between circadian timekeeping, female reproduction, and depressive-like symptoms in mice, and provide novel insight into the role of SCN VIP neurons.

Cocaine Effects on Reproductive Behavior and Fertility: An Overview

Cocaine is one of the most widely used drugs that, due to its molecular properties, causes various behavioral alterations, including sexual behavior. In vivo and in vitro studies conducted mainly in mammals have shown various disorders of sexual activity and morpho-functional dysfunctions of the gonads in both sexes. Although the modalities are still unclear, cocaine has been shown to alter the cell cycle, induce apoptosis, and alter sperm motility. In females, this drug alters the formation of the meiotic spindle as well as may obstruct the ovulation mechanism of mature oocytes. The data provided in this review, in addition to reviewing the current literature on the main effects of cocaine on spermatogenesis and oogenesis mainly in mammals, will hopefully provide a basic overview that may help and support further future studies on the molecular interaction of cocaine and its metabolites with germ cells.

Spermatogenesis and regulatory factors in the wall lizard Podarcis sicula

Spermatogenesis is an extraordinarily complex process, regulated by several factors, which leads to the differentiation of spermatogonia into spermatozoa. Among vertebrates, several reports have been focused on the lizard Podarcis sicula, a seasonal breeder and a good model for the study of reproductive processes. The goal of this review is to resume all the available data about systemic and above all local control factors involved in the control of P. sicula testicular activity. During the seasonal reproductive cycle, the variation of the expression levels of these factors determines significant variations that induce the activation or blocking of spermatogenesis. The data supplied in this review, in addition to analyze the current literature regarding the main actors of Podarcis sicula spermatogenesis, will hopefully provide a basic model that can be used for further studies on the intratesticular interaction between molecular factors that control spermatogenesis.

Alzheimer's Disease Mouse as a Model of Testis Degeneration

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with protective functions in the central nervous system and various peripheral organs. PACAP has the highest expression level in the testes, among the peripheral organs, and has a positive regulative role in spermatogenesis and in sperm motility. In the present study, we explored testicular degenerative alterations in a mouse model of Alzheimer’s disease (AD) (B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J) and demonstrated changes in PACAP-regulated signaling pathways. In addition, the effects of increased physical activity of AD (trained AD (TAD)) mice on testis were also followed. Reduced cell number and decreased thickness of basement membrane were detected in AD samples. These changes were compensated by physical activity. Expression of PACAP receptors and canonical signaling elements such as PKA, P-PKA, PP2A significantly decreased in AD mice, and altered Sox transcription factor expression was also detected. Via this signaling mechanism, physical activity compensated the negative effects of AD on the expression of type IV collagen. Our findings suggest that the testes of AD mice can be a good model of testis degeneration. Moreover, it can be an appropriate organ to follow the effects of various interventions such as physical activity on tissue regeneration and signaling alterations.

Immunolocalization of aromatase P450 in the epididymis of Podarcis sicula and Rattus rattus

The goal of this study was to evaluate P450 aromatase localization in the epididymis of two different vertebrates: the lizard Podarcis sicula, a seasonal breeder, and Rattus rattus, a continuous breeder. P450 aromatase is a key enzyme involved in the local control of spermatogenesis and steroidogenesis and we proved for the first time that this enzyme is represented in the epididymis of both P. sicula and R. rattus. In details, P450 aromatase was well represented in epithelial and myoid cells and in the connective tissue of P. sicula epididymis during the reproductive period; instead, during autumnal resumption this enzyme was absent in the connective tissue. During the non-reproductive period, P450 aromatase was localized only in myoid cells of P. sicula epididymis, whereas in R. rattus it was localized both in myoid cells and connective tissue. Our findings, the first on the epididymis aromatase localization in the vertebrates, suggest a possible role of P450 aromatase in the control of male genital tract function, particularly in sperm maturation.

Pituitary adenylate cyclase-activating peptide (PACAP) and its receptors in Mus musculus testis

To enlighten the involvement of PACAP/receptors system in the control of mammal testis, we investigated the expression of PACAP and the localization of PACAP and its receptors PAC1, VPAC1, and VPAC2 in the testis of Mus musculus. By molecular and immunohistochemical investigations, we highlighted that PACAP and its receptors are widely represented in germ cells of Mus testis, particularly in spermatocytes I, spermatids, and spermatozoa, strongly suggesting their involvement in spermatogenesis process. Moreover, for the first time in the adult mouse testis we highlighted that PACAP is present within Leydig cells, as PACAP receptors, confirming its involvement in the control of steroidogenesis in mouse.

Testicular steroidogenic enzymes in the lizard Podarcis sicula during the spermatogenic cycle

Steroidogenic Acute Regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-hydroxysteroid dehydrogenase (17β-HSD), 5α-Reductase (5α-Red), P450 aromatase are key enzymes involved in steroidogenesis. Recently, we showed the expression and the localization of P450 aromatase in Podarcis sicula testis during the different phases of the reproductive cycle, showing its involvement in the control of steroidogenesis, particularly in 17β-estradiol synthesis. Now, we have investigated the presence and distribution of the other enzymes involved in steroidogenesis, i.e. StAR, 3β-HSD, 17β-HSD and 5α-Red, during three significant periods of the reproductive cycle: summer stasis (July-August), autumnal resumption (November) and reproductive period (May-June). We demonstrated for the first time that all these enzymes are always present in somatic cells (Leydig and Sertoli) and germ cells (spermatogonia, spermatocytes I and II, spermatids and spermatozoa) of Podarcis testis, mainly in spermatids and spermatozoa. The present results strongly suggest that in Podarcis testis both somatic and germ cells could be involved in local sex hormone synthesis and that 5α-Red and P450 could carry out a pivot role.

Disturbed spermatogenic signaling in pituitary adenylate cyclase activating polypeptide-deficient mice

PACAP is a neuropeptide with diverse functions in various organs, including reproductive system. It is present in the testis in high concentrations, and in addition to the stage-specific expression within the seminiferous tubules, PACAP affects spermatogenesis and the functions of Leydig and Sertoli cells. Mice lacking endogenous PACAP show reduced fertility, but the possibility of abnormalities in spermatogenic signaling has not yet been investigated. Therefore, we performed a detailed morphological analysis of spermatozoa, sperm motility and investigated signaling pathways that play a role during spermatogenesis in knockout mice. No significant alterations were found in testicular morphology or motility of sperm in homozygous and heterozygous PACAP-deficient mice in spite of the moderately increased number of severely damaged sperms. However, we found robust changes in mRNA and/or protein expression of several factors that play an important role in spermatogenesis. Protein kinase A expression was markedly reduced, while downstream phospho-ERK and p38 were elevated in knockout animals. Expression of major transcription factors, such as Sox9 and phospho-Sox9, was decreased, while that of Sox10, as a redundant factor, was increased in PACAP-deficient mice. The reduced phospho-Sox9 expression was partly due to increased expression and activity of phosphatase PP2A in knockout mice. Targets of Sox transcription factors, such as collagen type IV, were reduced in knockout mice. In summary, our results show that lack of PACAP leads to disturbed signaling in spermatogenesis, which could be a factor responsible for reduced fertility in PACAP knockout mice, and further support the role of PACAP in reproduction.

P450 aromatase: a key enzyme in the spermatogenesis of the Italian wall lizard, Podarcis sicula

P450 aromatase is a key enzyme in steroidogenesis involved in the conversion of testosterone into 17β-estradiol. We investigated the localization and the expression of P450 aromatase in Podarcis sicula testes during the different phases of the reproductive cycle: summer stasis (July–August), early autumnal resumption (September), middle autumnal resumption (October–November), winter stasis (December–February), spring resumption (March–April) and the reproductive period (May–June). Using immunohistochemistry, we demonstrated that the P450 aromatase is always present in somatic and germ cells of P. sicula testis, particularly in spermatids and spermatozoa, except in early autumnal resumption, when P450 aromatase is evident only within Leydig cells. Using real-time PCR and semi-quantitative blot investigations, we also demonstrated that both mRNA and protein were expressed in all phases, with two peaks of expression occurring in summer and in winter stasis. These highest levels of P450 aromatase are in line with the increase of 17β-estradiol, responsible for the spermatogenesis block typical of this species. Differently, in autumnal resumption, the level of P450 aromatase dramatically decreased, along with 17β-estradiol levels, and testosterone titres increased, responsible for the subsequent renewal of spermatogenesis not followed by spermiation. In spring resumption and in the reproductive period we found intermediate P450 aromatase amounts, low levels of 17β-estradiol and the highest testosterone levels determining the resumption of spermatogenesis needed for reproduction. Our results, the first collected in a non-mammalian vertebrate, indicate a role of P450 aromatase in the control of steroidogenesis and spermatogenesis, particularly in spermiogenesis.

Role of PACAP on testosterone and 17β-estradiol production in the testis of wall lizard Podarcis sicula

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide that in mammalian testis is involved in the control of testosterone and 17β-estradiol synthesis. A similar involvement was recently postulated in the testis of a nonmammalian vertebrate, the wall lizard Podarcis sicula. Indeed, we reported the presence of PACAP and its receptors throughout the reproductive cycle within both germ and somatic cells. Now, we investigated the effects of PACAP on steroidogenesis in significant periods of Podarcis reproductive cycle: winter stasis, reproductive period and summer stasis. Using different in vitro treatments, in the absence or presence of receptor antagonists, we demonstrated that in P. sicula testis PACAP is involved in the control of testosterone and 17β-estradiol production. In particular we demonstrated that treatment with PACAP induced a testosterone increase only in stasis periods (winter and summer stasis); differently they induced a 17β-estradiol production in all periods analyzed (summer stasis, winter stasis and reproductive period).

PACAP and PAC₁ receptor in the reproductive cycle of male lizard Podarcis sicula

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide involved in multiple functions, including vertebrate reproduction. Recently, we reported the presence of PACAP in the testis of Italian wall lizard Podarcis sicula during reproductive period (May-June). Herein we investigated the PACAP mRNA expression and the localization of PACAP/PACAP receptor system, in the other periods of the Podarcis reproductive cycle, namely in summer stasis, early autumnal resumption, mid-autumnal resumption, winter stasis, and spring resumption. Using biomolecular and immunohistochemical investigations, we demonstrated that PACAP mRNA was widely expressed in all germ and somatic cells; in summer stasis (July-August) and early autumnal resumption (September) in particular, the mRNA was always found in Sertoli cells while was transiently expressed in germ and in Leydig cells. Differently from the mRNA, the protein was always present in germ and somatic cells independently from the reproductive cycle phase. As PACAP, the PAC1 receptor was always present in the testis, except for the summer stasis (July-August) and the early autumnal resumption (September), when PACAP was lacking in germ and somatic cells (Leydig and Sertoli cells). The present results strongly suggest that PACAP/PAC1 receptor system is widely represented during the reproductive cycle of male lizard. The possible involvement of PACAP/PACAP receptor system in the control of spermatogenesis is discussed.

Distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) in the human testis and in testicular germ cell tumors

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide expressed in the central nervous system and peripheral organs. Previous studies revealed the role and distribution of PACAP in the rodent testis, however, its presence in the human testis and in testicular germ cell tumors is not known. We used RT-PCR and immunohistological observations to investigate whether human testicular tissue and testicular germ cell tumors contain PACAP. The mRNAs for PACAP and its receptors were detected in total RNA extracted from human testes. PACAP immunoreactivity was observed in spermatogonia and spermatids from normal testes. In contrast, diffuse PACAP immunopositivity was observed in seminoma tumor cells, while only faint immunoreactivity was observed in embryonal carcinoma cells. Our data suggest that PACAP may play a role in human spermatogenesis and in testicular germ cell tumor development.

[A decrease of sensitivity of adenylyl cyclase and heterotrimeric G-proteins to chorionic gonadotropin and peptide hormones action in the tissues of reproductive system of the rats in the condition of experimental type 2 diabetes]

Patients with different forms of the diabetes, particularly with insulin-independent type 2 diabetes have a wide spectrum of the disturbances of the functions of reproductive system. It is supposed that the main reason of these disturbances is altered sensitivity of reproductive system tissues to regulatory action of hormones. The aim of the work was the identification of the changes in functioning of human chorionic gonadotropin (hCG)--and peptide hormones-sensitive adenylyl cyclase system (ACS) in the ovary, testes and uterus of rats with neonatal streptozotocin (STZ) diabetes that is similar to the type 2 diabetes in humans. The effects of hCG, PACAP-38 and relaxin, realizing their effects via G-protein of the stimulatory type (Gs), and somatostatin, acting via G-protein of the inhibitory type (Gi), on adenylyl cyclase (AC) activity and the GTP binding of the G-proteins were studied. Regulatory effects of hCG and PACAP-38 decreased in the ovary and testes of rats with STZ type 2 diabetes, while the effects of somatostatin decreased in all investigated tissues (in a considerable extent in the uterus). This expressed in the weakening of hormonal effects on AC activity, stimulating in the case of hCG and PACAP-38 and inhibiting in the case of somatostatin, and in the decrease of stimulation of the GTP binding by the hormones. At the same time a significant decrease of ACS sensitivity to relaxin in the tissues of diabetic rats was not found. Data obtained suggest that the key reason of the disturbances of reproductive functions in experimental type 2 diabetes is the decrease of ACS sensitivity to the hormones, such as hCG, PACAP-38 and somatostatin, that play a important role in functioning of reproductive system.

Expression of Neuropeptide Y gene in mouse testes during testicular development

AIM

To elucidate the distribution and regulation of Neuropeptide Y (NPY) gene expression in testes under physiological and pathophysiological conditions, such as testicular development, fasting and experimental cryptorchidism.

METHODS

In the first experiment, C57BL/6J male mice at the ages of 3 days as well as 2, 3, 5 and 8 weeks were used. In the second and third experiments, adult C57BL/6J male mice were subjected to fasting for 48 h and experimental cryptorchidism for 72 h. The NPY transcripts were detected by isotopic in situ hybridization histochemistry.

RESULTS

The NPY transcripts were exclusively expressed in the interstitial cells regardless of the age groups and experimental conditions. The NPY mRNA levels were found to increase significantly with age (from the neonatal to prepubertal period [P<0.01] and from the prepubetal to postpubertal period [P<0.01]). Food deprivation for 48 h resulted in a significant increase in the NPY mRNA levels in the arcuate nucleus of the hypothalamus (P<0.01), but not in the testes. Experimental cryptorchidism for 72 h failed to regulate the NPY gene expression in the testes.

CONCLUSION

NPY gene expression is distributed in Leydig cells and increases in line with testicular development. The regulation of testicular NPY is different from that of hypothalamic NPY.

Testicular growth hormone (GH): GH expression in spermatogonia and primary spermatocytes

Growth hormone (GH) gene expression is not restricted to pituitary somatotrophs and has recently been demonstrated in a variety of extrapituitary sites in mammals and the domestic chicken. The possibility that GH gene expression occurs in the male reproductive system of chickens was therefore examined, since GH has established roles in male reproductive function and GH immunoreactivity is present in the chicken testis. Using RT-PCR and oligonucleotide primers for pituitary GH cDNA, GH mRNA was shown to be present in the testes and vas deferens of adult cockerels. Although testicular GH mRNA was of low abundance (not detectable by Northern blotting), a 690 bp fragment of the amplified testicular GH cDNA was cloned and had a nucleotide sequence 99.6% homologous with pituitary GH cDNA. GH mRNA was localized by in situ hybridization in spermatogonia and primary spermatocytes of the seminiferous tubules, but unlike testicular GH-immunoreactivity, GH mRNA was not present in secondary spermatocytes, spermatids or spermatozoa. The presence of Pit-1 mRNA in the male reproductive tract may indicate Pit-1 involvement in GH expression in these tissues. The presence of GH receptor mRNA in the testis and vas deferens also suggests they are target sites for GH action. These results demonstrate, for the first time, expression of the pituitary GH gene in the testis, in which GH mRNA was discretely localized in primary spermatocytes. The local expression of the GH gene in these cells suggests autocrine or paracrine actions of GH during spermatogenesis.

Secretin Controls Anion Secretion in the Rat Epididymis in an Autocrine/Paracrine Fashion1

There is growing evidence that secretin, the first hormone discovered in our history, has functions in the brain other than in the gastrointestinal tract. This article reports for the first time that secretin and its receptor mRNAs are produced in distinct cell types within the epididymis. To test if secretin affects electrolyte transport in the epididymis, we measured short-circuit current (Isc) in cultured epididymal epithelia and found secretin dose-dependently stimulated Isc. Ion substitution experiments and use of pharmacological agents inferred that the stimulated Isc is a result of concurrent electrogenic chloride and bicarbonate secretion. It is further shown that secretin and pituitary adenylate cyclase-activating polypeptide (PACAP) function via totally different mechanisms: 1) PACAP works only from the apical side of the epithelium to stimulate chloride and not bicarbonate secretion, while secretin acts on the apical and basolateral sides to stimulate chloride and bicarbonate secretion. 2) the stimulation by PACAP but not secretin requires local prostaglandin synthesis. By immunocytochemical staining, secretin is localized in the principal cells of the initial segment and caput epididymidis, whereas secretin receptor is present in the principal cells of the proximal as well as the distal part of the epididymis. This pattern of distribution appears to be consistent with the idea that secretin is secreted by the proximal epididymis and acts on the proximal and distal epididymis in an autocrine and paracrine fashion. Its function is to control secretion of electrolytes and water.